Water and wastewater treatment processes sometimes use ballasted flocculation to clarify water or wastewater. A ballasted flocculation process allows for faster settling of the flocculated material that is formed in the process. The faster settling of the ballasted floc allows for very high overflow rates in the clarifier or settling tank, and therefore allows the footprint of the total treatment system to be significantly smaller than conventional clarifiers. Furthermore, compared to other conventional clarification systems, start-up and optimation times for ballasted flocculation systems are generally shorter due to the decreased hydraulic retention times of the system.
Ballasted flocculation treatment systems employ a physical/chemical process and remove mostly particulate and colloidal solids present in the raw water or wastewater stream. Due to the physical/chemical nature of the solids removed, often times the process does not remove dissolved constituents. Of particular interest in treating water or wastewater is soluble BOD. Soluble BOD and particulate BOD are components of total BOD. While ballasted flocculation processes may achieve greater than 85% particulate BOD removal, these processes do not efficiently remove soluble BOD.
Therefore, there has been and continues to be a need for a ballasted flocculation system that will effectively remove soluble BOD.